PAR
From The Aquarium Wiki
Photosynthetically Active Radiation. In the aquarium hobby this is the closest measure of useable light.
What is PAR?[edit]
PAR is a measure of light from the 400 to 700 nanometer ranges. With emphasis on the colors of the specturm that matter most to photosynthetic creatures. PAR can be measured by a PAR meter or a Quantum meter.
